Batteries have been proposed as a clean, efficient and environmentally responsible power source for electric vehicles, and various other applications. They are also becoming more popular for large-scale energy storage, providing frequency regulation or auxiliary power to the power grid and allowing better use of intermittent power generation from sources like wind turbines and solar panels.
Battery cells, and in particular, lithium ion cells, are known to generate heat when charging or discharging. Overheating or an exposure to high temperatures may undesirably affect the functioning and lifespan of a battery system. Thus battery systems typically employ some form of cooling system.
Many systems use some form of air cooling, mainly due to convenience. These are shown, for instance, in U.S. published application 2003/0211384 published Nov. 13, 2003, U.S. published application 2006/0080986A1 published Apr. 20, 2006 and U.S. published application 2007/0102213 published May 10, 2007 incorporated herein by reference. An additional benefit of these cooling systems is that air is not electrically conducting and as such will not cause short circuits. However, air has a low thermal conductivity and a low heat capacity; thus air cooling systems exhibit inadequate efficiency for use with larger batteries.
Another common setup is to include tubes or channels to conduct a cooling fluid between the individual cells in a battery module. Because aqueous fluids are most commonly used, and aqueous fluids are generally conductive, leaks in these systems can be very damaging to the battery system. To ensure fluid-tight joining of the parts and components and to minimize susceptibility to leakage, processes and equipment used to assemble this type of cooling system are highly automated, complex, and have costs for manufacture and maintenance.
An additional concern is the temperature distribution throughout a cell or battery module. Cell temperature affects charging efficiency and capacity; lower capacity can lead to over-discharging, which will lower the operational lifespan of the cell and the battery as a whole. Batteries with greater temperature uniformity tend to operate more efficiently and have longer operating lives.
A further difficulty with larger electric chemical battery cells is that different parts of the batteries themselves may have different localized temperatures. This is the case for a number of reasons including the physical size of the cells themselves, the poor thermal conductivity within the cells themselves, and the fact that some sections of the cells may generate more heat than other sections. In other words, specific parts of the cells may have different localized temperatures requiring different cooling to avoid undesirable effects.
Therefore, there is a need in the art for a battery module which efficiently removes heat from the battery cells and produces a more uniform temperature distribution amongst the battery cells, while providing the necessary functionality with respect to containment and protection.